The present invention generally concerns a paper feeder for use in an office automation (O/A) system such as a copying machine or a facsimile system and, more particularly, a device for feeding stacked documents accurately one by one.
FIG. 1 illustrates a conventional document feeding device for a facsimile, the device comprises a table 11 for loading the stacked documents, 20 a pick-up roll 12 for picking up the lowermost document of the stacked documents, and a pick-up rubber 14 for cooperating with the pick-up roll 12 so, as to only convey the lowermost document into the facsimile. The free end portion of the pick-up rubber 14 is pressed against a portion of the surface of the pick-up roll 12 by a compression spring 13 via a pressure plate 16. Under the pressure plate 16 is fixedly mounted plate spring 15, whose end portion is smoothly curved up-wardly. The underside of the curved portion of the plate spring 15 contacts the circumferential surface of the pick-up roll 12 at a point thereof.
In feeding the documents, the stacked documents on the table 11 approach separating position B, the approach is sensed by a sensing device (not shown), and thus, the pick-up roll 12 is driven to convey the lowermost document of the stacked documents. The leading end of the conveyed document approaches the separating position B after passing under the plate spring 15, and therefore, the frictional force between the document and the surface of the pick-up roll 12 is increased over that when the document simply contacts the separating position B. Thus, as the contact are between the document and the pick-up roll 12 is increased so as to increase the frictional force, the paper feeder correspondingly ensures the document conveying. In this case, the front surface of the document contacts the pick-up roll 12, while the back surface of the document contacts the pick-up rubber 14. Thus, the front surface of the document contacts the pick-up roll 12 from position A, while the back surface of the document contacts the pick-up rubber 14 from position B. Consequently, the frictional force between the document and the pick-up roll 12 becomes greater than that between the document and the pick-up rubber 14, so that the document just contacting the pick-up roll 12 may be conveyed forwardly, and the remaining documents are prevented from being conveyed just before the separating position B.
When the leading end of the document passing the separating position B passes under the plate spring 15, the contact between the document and the pick-up roll 12 is more improved, thereby more ensuring the document conveying. Thus, the documents are sequentially conveyed one by one by the rotation of the pick-up roll 12.
In such a conventional document feeding device, the document feeding condition is influenced by the kind, size and number of the documents, and the frictional force between the documents and the pick-up rubber 14 is influenced by the temperature and humidity of the surrounding atmosphere, so that the document conveying frequently experiences poor conditions Moreover, long use of the pick-up roll 12 results in changes in the frictional coefficient of the roll and the hardness of the roll material, thereby deteriorating the document feeding